Effect of Sowing Date and Cultivar on Root System Development in Pea (Pisum sativum L.)

In many species, root system development depends on cultivar and sowing date, with consequences for aerial growth, and seed yield. Most of the peas (Pisum sativum L.) grown in France are sown in spring or in mid-November. We analyzed the effect of two sowing periods (November and February) and three pea cultivars (a spring cultivar, a winter cultivar, a winter recombinant inbred line) on root development in field conditions. For all treatments, rooting depth at various dates seemed to be strongly correlated with cumulative radiation since sowing. Maximum root depth varied from 0.88 to 1.06 m, with the roots penetrating to greater depths for February sowing than for November sowing in very cold winters. The earlier the crop was sown, the sooner maximum root depth was reached. No difference in root dynamics between cultivars was observed. In contrast, the winter recombinant inbred line presented the highest root density in the ploughed layer. These findings are discussed in terms of their possible implications for yield stability and environmental impact.     

Soil compaction and the growth of vining peas

The effects of differing soil conditions at two sites on the growth of vining peas are described. The work was carried out over several seasons having contrasting rainfall at the time of crop emergence. Topsoil compaction induced by tractor wheelings reduced plant population and yield of vining peas by up to 70%. On the compacted plots peas were unable to compensate for the low population which was demonstrated by the inclusion of a non-compacted treatment thinned to the same population as the compacted plots. The severity of compaction was greatest when soil conditions were dry at emergence and least severe when wet. It is suggested that compaction resulted in increased ethylene production in the root and shoot tissues and this may be a causal agent of the observed growth modifications. Recultivation of a compacted seed bed prior to sowing resulted in better establishment and higher yields than with the topsoil compacted but final yields were variable when compared to a ploughed control. Double digging did not increase yield above a ploughed control. In one year a 25% yield reduction was attributed to this treatment. The reasons for the reduction in yield are complex but it is suggested that the causal agent was modfied soil and plant water relations resulting in altered crop physiology. Tramlining the crop reduced yield in one year but when the frequency of wheeling damage is considered they would be unlikely to affect productivity.     

Fibrous carrot root responses to irrigation and compaction of sandy and organic soils

Field experiments were performed in Southern Finland on fine sand and organic soil in 1990 and 1991 to study carrot roots. Fall ploughed land was loosened by rotary harrowing to a depth of 20 cm or compacted under moist conditions to a depth of 25–30 cm by three passes of adjacent wheel tracks with a tractor weighing 3 Mg, in April were contiguously applied across the plot before seed bed preparation. Sprinkler irrigation (30 mm) was applied to fine sand when moisture in the 0–15 cm range of soil depth was 50% of plant-available water capacity. For root sampling, polyvinyl chloride (PVC) cylinders (30 × 60 cm) were installed in the rows of experimental plots after sowing, and removed at harvest. Six carrot plants were grown in each of in these soil colums in situ in the field.Fine root length and width were quantified by image analysis. Root length density (RLD) per plant was 0.2–1.0 cm cm^-3 in the 0–30 cm range. The fibrous root system of one carrot had total root lengths of 130–150 m in loose fine sand and 180–200 m in compacted fine sand. More roots were observed in irrigated than non-irrigated soils. In the 0–50 cm range of organic soil, 230–250 m of root length were removed from loosened organic soils and 240–300 m from compacted soils. Specific root surface area (surface area divided by dry root weight) of a carrot fibrous root system averaged 1500–2000 cm² g^-1. Root length to weight ratios of 250–350 m g^-1 effectively compare with the ratios of other species.Fibrous root growth was stimulated by soil compaction or irrigation to a depth of 30 cm, in both the fine sand and organic soils, suggesting better soil water supply in compacted than in loosened soils. Soil compaction increased root diameters more in fine sand than it did in organic soil. Most of the root length in loosened soils (fine sand 90%, organic soil 80%) and compacted soils (fine sand 80%, organic soil 75%) was composed of roots with diameters of approximately 0.15 mm. With respect to dry weight, length, surface area and volume of the fibrous root system, all the measurements gave significant resposes to irrigation and soil compaction. Total root volumes in the 0–50 cm of soil were 4.3 cm³ and 9.8 cm³ in loosened fine sand and organic soils, respectively, and 6.7 cm³ and 13.4 cm³ in compacted sand and organic soils, respectively. In fine sand, irrigation increased the volume from 4.8 to 6.3 cm³.     

Oat residue and soil compaction influences on common root rot (Aphanomyes euteiches) of peas in a fine-textured soil

Management of common root rot (Aphanomyces euteiches Drechs.) in peas (Pisum sativum L.) is sought primarily by host crop avoidance for several years. Soil compaction is known to aggravate A. euteiches disease in peas but effects on infection and subsequent symptom development are not sufficiently known to assist in cultural control. Several isolated observations have noted that oat crop residues may suppress A. euteiches infection and disease in pea roots. The individual and combined influence (a factorial combination of two factors each at two levels) of a prior oat crop and soil compaction were studied for their effects on common root rot severity in processing peas grown in an A. euteiches disease nursery on a fine-textured soil in the northern Corn Belt of the USA. A previous crop of summer oats relative to prior-year peas significantly suppressed common root rot and increased pea fresh vine weight 210% at peak bloom stage. Both fresh vine weight and green pea yield were reduced as much as 63% by soil compaction and increased as much as 48% by a prior oat crop. Greater soil bulk density at the 10 to 25-cm depth identified wheel traffic compaction patterns in each year. A 10-fold reduction of saturated hydraulic conductivity in the 10 to 25-cm compacted zone and high soil-water potentials within the upper 60 cm both confirmed an impaired water drainage, especially during infiltration events. These observations support the use of a previous full season or summer oat crop jointly with chisel plowing, plus the prevention of excessive traffic during secondary tillage and planting, to reduce common root rot in a field infested with A. euteiches. Shallow incorporation of oat shoot and root residue by chiseling could be a crucial component of the cultural control of the disease. R Rodriguez Kabana Section editor     

The root activity of cereals and peas when grown in pure stands and mixtures

Lithium was used as a non-radioactive tracer to investigate the root activity of two cereals (wheat and barley), and of two contrasting cultivars of pea (leafy and semi-leafless), both in pure stands and in mixtures. The mixtures included combinations of each cereal with each pea cultivar in single rows, alternative rows and cross-drilled. Total lithium uptake (mg m^-2) was higher for wheat than for barley, and higher for semi-leafless pea than for leafy peas. Growing cereals with peas reduced the total lithium uptake by peas, compared with pure stands, especially in alternate-row mixtures. Growing peas with cereals only reduced the total Li uptake by cereals when they were cross-drilled. The Li uptake by wheat, barley and peas generally decreased with soil depth in a similar manner; however, semi-leafless peas absorbed proportionately more Li from close to the soil surface than did leafy peas. Both pea cultivars absorbed more Li at 10–20 cm depth when grown in intimate mixtures with cereals, compared with less intimate mixtures or pure stands. The potential of lithium as a non-radioactive tracer in mixed-cropping studies is briefly discussed.     

Development of pea bacterial blight caused by Pseudomonas syringae pv. pisi in winter and spring cultivars of combining peas (Pisum sativum) with different sowing dates

Pea bacterial blight occurred by natural infection in a field trial on peas in 1995. Disease development in the winter cultivars Rafale, Frilene and Froidure was compared with that in the spring cultivars Baccara, Conquest and Bohatyr, each sown on six dates in October, November, December, mid-March, late March and April. Disease incidence had reached 100% plants affected in all treatments by mid-July. Disease severity was greater in winter-sown (October, November or December) than in spring-sown peas of each cultivar at each assessment. Significant (P < 0.05) differences in disease severity occurred between cultivars in the winter-sown plots in May and June and the spring cultivars were affected more severely than the winter cultivars. Comparison of areas under the disease progress curves for both disease incidence and severity also showed that the winter-sown peas were more affected by disease than spring-sown peas and that spring cultivars were more severely affected than winter cultivars. Yield was strongly correlated with disease severity. A linear regression model suggested that, for peas sown in October, November or December, a yield loss of 0.5 tha^-1 occurred for each 10% increase in canopy area affected by pea bacterial blight.     

Effect of seed depth on slug damage to winter wheat

In a field experiment drilled at two depths on three dates in autumn 1988, with or without methiocarb pellets broadcast on the soil surface immediately after drilling, 26% of seeds of winter wheat sown at c. 20 mm depth were killed by slugs compared with only 9% of seeds sown at c. 40 mm. The protection from slug damage provided by this additional 20 mm of depth was comparable with that provided by methiocarb pellets. The effects of seed depth and pellet application did not interact and were consistent on all drilling dates. Thus, fewest seeds and seedlings were killed where methiocarb pellets were broadcast on a seed-bed with seeds sown at 40 mm depth. Intermediate damage was recorded where seeds were sown at 40 mm depth without pellets, or where pellets were broadcast on seeds sown at 20 mm depth. Most seeds and seedlings were killed where seeds were sown at 20 mm depth without pellets. Sublethal damage to seedlings was not affected by sowing depth but was reduced where pellets were broadcast immediately after sowing.     

Effects of temperature on the development and growth of winter wheat roots

Winter wheat was sown on 2 dates with 3 levels of nitrogen fiertiliser (0, 50 and 200 kg N ha⁻¹) in one year and on 2 sites in a followign season. Shoot and root development and growth were measured between emergence and anthesis in the first season and emergence and 7 mainstem leaves in the second. Differences in temperature and light regime led to significant differences in shoot and root development and growth between sowing dates. A thermal time-scale, based on soil surface or air temperatures, with a base of 0°C, adequately described the production of mainstem leaves and nodal root axes over all treatments. Autumn applied nitrogen had little effect on development. Shoot growth and green area index increased exponentially with thermal time prior to spring nitrogen application and the completion of canopy development. Early-sown crops had larger root systems than late-sown crops prior to winter and this divergence was retained until anthesis. The relationship between root growth and thermal time was little better than with days after sowing and was not improved by either varying the site of temperature measurement or the base temperature used for calculation. Differences in soil texture and drainage, between sites, led to significant changes in root length distribution. Although spring applied nitrogen generally increased root length, its effects were inconsistent. There was a curvilinear relation between root length and the amount of photosynthetically active radiation (PAR) intercepted; this relation was unaffected by sowing date or nitrogen treatment. The amount of root produced per unit PAR decreased as the season progressed, reflecting the decrease in the proportion of total dry matter partitioned to the root system.     

Spatial distribution of roots of pearl millet on sandy soils of Niger

Root sampling in crop stands of low planting density requires reliable information on horizontal distribution of roots. This applies particularly to pearl millet in the Sahel, which is sown at a rate of less than two pockets of seed per m². The objective of this study was to investigate the spatial variability of root length density (RLD) among sampling positions in an improved management system with ridging and under traditional sowing. RLD between ridges (bR) was lower compared to sampling positions within ridges (wR) at soil depth layers from 0 to 80 cm soil depth. We found a highly significant, positive correlation between the sum of the root length (RL) of four sampling dates (tillering, booting, flowering, and maturity) with shoot dry mass (SDM) at maturity. The square of the correlation coefficient was highest when calculation of RL was based on RLD at all four sampling positions. While SDM exhibited significant differences among three pearl millet varieties, sole root sampling wR at a lateral distance of 60 cm relative to the pocket would not allow for the detection of varietal differences in RL, while all other sampling positions did. The correlation between RL and SDM was considerably improved if information of RLD bR was included. Under traditional sowing, RLD directly under the plant was lower compared to sampling positions at lateral distance 25 and 50 cm from the centre of the pocket, but this effect of sampling position was not significant. RLD estimates within deeper soil layers were not systematically affected by direction and lateral distance. To obtain accurate information about depth of rooting and RL under traditional sowing, samples should be taken from lateral distances between 20 and 40 cm from the pocket centre.     

The influence of waterlogging at different temperatures on penetration depth and porosity of roots and on stomatal diffusive resistance of pea and maize seedlings

The 8 days old seedlings of pea (cv. Ilowiecki) and maize (cv. Alma F1) were subjected to differentiated aeration conditions (control — with pore water tension about 15 kPa and flooded treatment) for 12 days at three soil temperatures (7, 15 and 25 °C). The shoots were grown at 25 °C while the soil temperature was differentiated by keeping the cylinders with the soil in thermostated water bath of the appropriate temperature. Lowering the root temperature with respect to the shoot temperature caused under control (oxic) conditions a decrease of the root penetration depth, their mass and porosity as well as a decrease of shoot height, their mass and chlorophyll content; the changes being more pronounced in maize as compared to the pea plants. Flooding the soil diminished the effect of temperature on the investigated parameters; the temperature effect remaining significant only in the case of shoot biomass and root porosity of pea plants. Root porosity of pea plants ranged from 2 to 4 % and that of maize plants — from 4 to 6 % of the root volume. Flooding the soil caused an increase in the root porosity of the pea plants in the entire temperature range and in maize roots at lower temperatures by about 1 % of the root volume. Flooding the soil caused a decrease of root mass and penetration depth as well as a decrease of plant height, biomass and leaf chlorophyll content.     

The effect of soil compaction on germination and early growth of Eucalyptus albens and an exotic annual grass

Most agricultural land has been compacted to some degree by heavy machinery or livestock trampling. This legacy is expected to influence the success of tree seedling recruits in farmland areas where natural regeneration is being encouraged. We investigated the impact of soil compaction on seedlings of a woodland eucalypt (Eucalyptus albens) and an annual grass competitor (Vulpia myuros) in a laboratory experiment. Replicate soil cores were created at five bulk density levels; 1.0, 1.1, 1.2, 1.3 or 1.4 Mg m^?3 with a soil water content of 20%. The depth of root penetration declined linearly with increasing bulk density, resulting in a decrease in root depth of around 75% in the most compacted soil compared with the least compacted soil for both species. Shoot length and primary root length did not vary between soil bulk density levels for either species, but seedlings responded to increasing levels of compaction with oblique (non‐vertical) root growth. Results suggest that young seedlings of both E. albens and V. myuros will be more susceptible to surface drying in compacted than uncompacted soils and therefore face a greater risk of desiccation during the critical months following germination. Any competitive advantage that V. myuros may have over E. albens is not evident in differential response to soil compaction.     

Growth and development of root systems of winter cereals grown after different tillage methods including direct drilling

Summary A method is described for rapidly estimating the depth of penetration and density of roots of cereal crops under field conditions. Counts of living roots, traversing horizontal faces of soil cores, were made for winter wheat growing on direct-drilled and ploughed land.The rate of penetration of roots of winter wheat in a clay and a sandy loam soil averaged 5 mm per day throughout winters without extremes of cold or wet. Death of roots near the soil surface occurred wilst others continued downward penetration. The rate of root elongation was slower during prolonged periods when the soil was wet and faster,i.e. to greater depths, during dry conditions.Damage sustained to roots during adverse winter conditions ofter varied between direct drilling and ploughing. More roots at depth were consistently recorded on direct-drilled than on ploughed land when measured in spring after a soil water deficit had developed during the preceding month. After prolonged wet soil conditions during the winter on a soil with a large clay fraction and low hydraulic conductivity, root growth and penetration in spring, before the development of a soil water deficit, was more restricted on direct-drilled than on ploughed land.     

Prevention of aluminium toxicity with supplemental boron. II. Stimulation of root growth in an acidic, high-aluminium subsoil

Root growth inhibition is an early symptom of Al toxicity and B deficiency. Our hypothesis is that Al toxicity may induce B deficiency, and it was our objective to determine if incorporation of supplemental B would promote root penetration into an acidic, high-Al subsoil. Alfalfa (Medicago sativa L. cv. Hy-Phy) was grown in slanted tubes with a Plexiglas window along their length. The top half of the tub contained silt loam soil and the bottom half contained subsoil from the Bt1 horizon (26% Al saturation) of a Creldon silty clay loam. Both soils originally contained 0–9 kg B ha^?1. When root growth was measured in the bottom half of the high-A1 subsoil, all measurements—depth of rooting, total root growth, final root lengths and root dry weight—demonstrated greater root growth in treatments where additional B was incorporated into the high-Al subsoil. Results from this soil study extend those obtained in our hydroponic study in which supplemental B presented Al inhibition of root growth. Boron concentrations may need to he increased under acidic ‘high-Al’ soil conditions to promote root penetration into these soil zones, and this could be especially important during periods of drought stress.     

Varietal differences in shoot and rooting parameters of pearl millet on sandy soils in Niger

Root parameters are important traits for the acquisition of nutrients and water under resource-limited conditions. In order to investigate the extent of varietal differences in rooting parameters in pearl millet, we compared a total of eight pearl millet varieties in two experiments (ridging and traditional sowing) over four years at the ICRISAT Sahelian Centre, Niger. We found substantial genotypic variation for root length density (RLD), root dry matter, and total root length (RL), but not for specific root length, depth of rooting, or partitioning of roots between topsoil and subsoil (>20 cm depth). RL showed a highly dynamic pattern over the growing season. RL and shoot dry matter were positively correlated over P supplies and contrasting levels of field productivity. The relationship between RL and grain yield as well as harvest index were less clear. The root fraction responded to variation in soil productivity, increasing from roughly 20% under high productivity to more than 40% at low productivity, but we found no evidence of varietal differences in this trait despite pronounced differences in maturity and plant stature. Identification of pearl millet varieties suited for growth under low input conditions in south-west Niger can potentially make use of existing genotypic variability in root parameters, but we suggest that, due to high variability for root traits, indirect selection for shoot parameters (e.g., number of stems) is more promising than direct selection for RLD or RL.     

Analysis of the spatial variability of maize root density

The spatial arrangement of maize roots was studied in a clay loam field in order to test the regularity of root arrangement, which is implicitly assumed when distances between neighbouring roots are calculated. For that. we carried out a mapping of root contacts on six superposed horizontal planes which cut the rooting volume of several area samples. Three situations were studied: (i) one inter-row out of two was compacted down to the base of the ploughed layer (28 cm), but not in non-tilled layers (28 to 200 cm); (ii) a mechanical obstacle was placed at the base of the ploughed layer; (iii) one inter-row out of two was compacted down to half the depth of the ploughed layer. On all horizontal planes, the spatial arrangement or root contacts followed a non-regular, clustered pattern for a 10⁻²m scale of study, even in parts of soil which had not been disturbed by compactions. In the first two situations, where obstacles met the base of the ploughed layer, root density in non-tilled layers was several times lower below the obstacles than below the remaining parts of the ploughed layer. This caused a 10⁻¹ m sized variability which was superimposed on to the 10⁻² m one. Conversely in the third situation, obstacles had no appreciable effect on root density in non-tilled layers. Obstacles located at the base of the ploughed layer therefore prevented root access to non-tilled layer and caused a ‘shadow effect’ in the non-tilled layers. This effect is probably due to the main vertical direction of roots in these layers.     

Rate of differentiation and emergence of nodal maize roots

The timing of root production is one of the parameters required for modelling the root system architecture. The objectives of this study are (1) to describe the rate of appearance of adventitious root primordia of maize and their rate of emergence out of the stem; (2) to test equations for the prediction of the rank of the phytomer on which root emergence occurs, in a wide range of field situations.Maize, cultivar Dea, was grown in controlled conditions and in the field in 1987, 1988, 1989 and 1991. Plants were regularly sampled and the following data were recorded: foliar stage, number of root primordia and number of emerged roots per phytomer. Root primordia were counted in transverse thin sections in the stem.At a single plant level, root primordia differentiation occurred sequentially on the successive phytomers, with no overlapping between two phytomers. The same was true for root emergence. Roots belonging to the same phytomer emerged at approximately the same time.At a plant population level, there was a linear relationship between the rank of the phytomer on which root primordia were differentiated and cumulated degree-days after sowing. A linear relationship was also observed between the rank of the phytomer on which roots were emerging and cumulated degree-days or foliar stage. In the range of field situations tested (several years, sowing dates and planting densities), both equations gave an accurate prediction of the timing of root emergence during the plant cycle.     

Capacity of biological soil crusts colonized by the lichen <Emphasis Type="Italic">Diploschistes</Emphasis> to metabolize simple phenols

Background and aims

Soil compaction strongly affects water uptake by roots. The aim of the work was to examine soil—plant interactions with focus on the impact of distribution of compacted soil layers on growth and water uptake by wheat roots.

Methods

The growth-chamber experiment was conducted on wheat growth in soil with compacted soil layers. The system for maintaining constant soil water potential and measurement of daily water uptake from variously compacted soil layers was used.

Results

Layered soil compaction differentiated vertical root distribution to higher extent for root length than root mass. The propagation rate of a water extraction front was the highest through layers of moderately compacted soil. The root water uptake rate was on average 67 % higher from moderately than heavily compacted soil layers. Correlations between water uptake and the length of thick roots were increasing with increasing level of soil compaction.

Conclusions

The study shows that root amount, water uptake, propagation of water extraction and shoot growth strongly depend on the existence of compacted layers within soil profile. The negative effects of heavily compacted subsoil layer on water uptake were partly compensated by increased uptake from looser top soil layers and significant contribution of thicker roots in water uptake.     

Effectiveness of rhizobacteria containing ACC deaminase for growth promotion of peas (Pisum sativum) under drought conditions

A series of experiments were conducted to assess the effectiveness of rhizobacteria containing 1-aminocyclopropane- 1-carboxylate (ACC) deaminase for growth promotion of peas under drought conditions. Ten rhizobacteria isolated from the rhizosphere of different crops (peas, wheat, and maize) were screened for their growth promoting ability in peas under axenic condition. Three rhizobacterial isolates, Pseudomonas fluorescens biotype G (ACC-5), P. fluorescens (ACC-14), and P. putida biotype A (Q-7), were selected for pot trial on the basis of their source, ACC deaminase activity, root colonization, and growth promoting activity under axenic conditions. Inoculated and uninoculated (control) seeds of pea cultivar 2000 were sown in pots (4 seeds/pot) at different soil moisture levels (25, 50, 75, and 100% of field capacity). Results revealed that decreasing the soil moisture levels from 100 to 25% of field capacity significantly decreased the growth of peas. However, inoculation of peas with rhizobacteria containing ACC deaminase significantly decreased the "drought stress imposed effects" on growth of peas, although with variable efficacy at different moisture levels. At the lowest soil moisture level (25% field capacity), rhizobacterial isolate Pseudomonas fluorescens biotype G (ACC-5) was found to be more promising compared with the other isolates, as it caused maximum increases in fresh weight, dry weight, root length, shoot length, number of leaves per plant, and water use efficiency on fresh and dry weight basis (45, 150, 92, 45, 140, 46, and 147%, respectively) compared with respective uninoculated controls. It is highly likely that rhizobacteria containing ACC deaminase might have decreased the drought-stress induced ethylene in inoculated plants, which resulted in better growth of plants even at low moisture levels. Therefore, inoculation with rhizobacteria containing ACC deaminase could be helpful in eliminating the inhibitory effects of drought stress on the growth of peas.     

Root turnover of groundnut (Arachis hypogaea L.) in soil tubes

Five groundnut cultivars were grown in transparent tubes of pasteurized loam compost in growth-chamber conditions. Weekly tracings were made of all the roots visible through the walls of the tubes. White roots were assessed as living, and brown or decayed roots as dead; this correlated with microscopical assessments of root viability based on cytoplasmic staining with neutral red followed by plasmolysis.For all five cultivars, root laterals began to die 3–4 weeks after plants were sown. Death of root laterals progressed down the soil profile with time, while new roots were produced successively deeper from the extending taproot. The half-life of individual roots was calculated as 3.7–4.4 weeks for all cultivars, based on assessments of the roots that died up to plant maturity (14–20 weeks, depending on cultivar). At maturity, 73–83% of the cumulative length of root systems had died. The onset and rate of root death were not related to onset of flowering or pod-filling; instead, the peak times of root death at different distances down the root system were related to earlier (3–5 week) peak times of root production in those regions. The net result of root turnover was that, despite continued new root production, the maximum length of living (white) roots of each cultivar was recorded at 2–4 weeks after sowing. Death of the earliest formed root laterals was also observed in the first five weeks after sowing of groundnut in an experimental field plot in Malawi. Progressive root turnover is considered to be a normal feature of groundnut, perhaps representing an energy-economy strategy.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.